1. Field of the Invention
This invention relates to a method of manufacturing a semiconductor device, and particularly to a method of manufacturing a semiconductor device, which is capable of reducing metal-film stress produced when a high melting-point metal film is formed by Chemical Vapor Deposition.
2. Description of the Related Art
There has heretofore been increasingly a demand for speeding up and micro-fabrication of a semiconductor device. As means for meeting this demand, it is known that a high melting-point metal (i.e., a refactory metal) is used for gate electrodes and conductive lines for the semiconductor device.
For example, a technique is known in which tungsten deposited by Chemical Vapor Deposition (abbreviated as "CVD") is used for conductive lines or interconnections.
It is known that a high melting-point metal film typified by such tungsten has strong tensile stress. This stress becomes more and more conspicuous due to heat treatment or the like after the formation of the high melting-point metal film.
As the tensile stress becomes great, a semiconductor wafer with the high melting-point metal film formed thereon increases in warpage. With the increase in the amount of warpage of the wafer, a deviation in focus occurs in a patterning process for forming conductive lines or interconnections, particularly an exposure process using a stepper, thus creating a difficulty in the formation of conductive lines or interconnections having desired dimensions. This problem remarkably occurs in a peripheral portion of the semiconductor wafer, which is most affected by the amount of warpage thereof.
As a method of solving the above difficulty, implantation of tungsten ions in a deposited tungsten film has been proposed in Japanese Patent Application Laid-Open No. Hei 8-97212 opened to the public in Apr. 12, 1996.
However, since metal ions typified by the tungsten ions are large in mass, controllability is very poor. Namely, it is very difficult to implant ions in a desired portion of a thin metal film.